RICHMOND, Va. -- A 16-year-old boy was charged Saturday in the assault of a young girl and the killing of her 8-year-old brother, who was apparently slain when he tried to protect her, authorities and relatives said.

The 8-year-old, Martin Cobb, was reportedly hit in the head with a brick during the attack near their home Thursday, neighbors told The Richmond Times Dispatch. Richmond Deputy Commonwealth's Attorney Mary E. Langer said she could not confirm a brick was used but police told her Martin suffered severe head trauma.

VIDEO: Prayer vigil for Martin Cobb, 8

The 12-year-old girl was taken to a hospital, but her injuries were not released by police. "As far as I know, she's doing fine. . She's doing better. She's OK," the siblings' aunt Geraldine Pitchford told the newspaper.

The 16-year-old boy was charged with murder and strangulation, police said in a news release. Authorities said he intimidated and threatened the girl and she initially gave authorities the wrong description of her attacker. Police did not immediately return a telephone message from The Associated Press.

Authorities were not identifying the teen because of his age. The AP also generally does not identify juveniles charged with crimes.

Pitchford described Martin as warm-hearted and friendly and said he was often playing with his sister outside.

"I'm proud of him. I'm proud that he stuck up for his sister. He did what he was taught," she said.

Pastor Dr. Theodore L. Hughey of the Abundant Life church said the boy, also known as "Marty" and "Little Martin," and his sister were inseparable and "always in and out" of the church.

"You saw one. The other was there. They were never apart," Hughey said.

Hundreds of people attended a vigil for Martin on Saturday night.

"He had a heart of a lion," said neighbor Andrew Patillo. "He stood so tall, to be so small."

Before the vigil began, loved ones gathered around a sign in Martin's yard near the church. "Martin: A real hero lived, fought and died here," the sign said.